The AT2 receptor is a developmentally regulated receptor that is up-regulated in adult cardiovascular tissues in response to injury. This receptor exerts growth inhibitory action on vascular smooth muscle cell (VSMC) in part via the activation of phosphotyrosine phosphatase and the inactivation of MAP kinase (ERK). We have shown that in PC12W cells and in VSMC, MKP-1 plays a critical role in the MAP kinase inactivation. The importance of AT2 receptor expression in the developmental biology of VSMC has been demonstrated in vitro and in vivo. Indeed, we demonstrated that cultured VSMC derived from AT2 receptor knock out mice at embryonic day 20 exhibits an exaggerated growth response to growth factors even in the absence of Ang II. Moreover, we showed that ERK plays a central role in this response. Taken together, these data suggest that the AT2 receptor expression influences fetal vasculogenesis via the programming of ERK cascade and subsequently the expression of growth modulating genes. The purpose of this proposal is to elucidate and identify, using genome technology, the genes whose expression are pivotal to AT2 receptor's action on growth modulation and development of VSMC. We expect to discover genes that play global and generalized roles in VSMC growth and development. Our specific aims are: 1) To employ gene array technologies to discover and characterize the genes whose expression are differentially regulated in neonatal VSMC derived from wild type and AT2 knockout mouse aorta. 2) To further identify the subject of those genes that are regulated by the ERK cascade. This will be accomplished by studying gene expression in above VSMC in the presence or absence of inhibitors of ERK pathway. 3) To use high throughput in vitro screening assays for cell proliferation and cell death to identify the function of the novel genes discovered in Aim 2. This will be accomplished by a gain of function (gene transfer) or loss of function (antisense) approaches. 4) To characterize expression patterns of these genes vivo during development and in vascular injury, and 5) to define the in vivo function of these novel genes with the production of recombinant mice.